This invention relates generally to improvements in a stabilizer for an earth structure, and more particularly to an improved stabilizer of the type employing a compressible tube for engagement with the surface of a bore formed in the earth structure.
The prior art teaches the use of a compressible tube for roof support, and teaches the use of the bore to compress the tube. A tube is forced into an undersized bore where it frictionally engages the surface of the bore to anchor itself.
In coal mines, it is generally necessary to leave a roof layer of top coal or shale through which a roof support pin must be mounted. This roof layer of top coal is quite fragile, and the force exerted on it by a tube being inserted into an undersize bore could result in the fracturing of the top coal, thereby causing it to either fall or create a very dangerous condition. It is therefore important that the bore opening not be used to compress a tube.
The stabilizer disclosed by U.S. Pat. No. 3,349,567 discloses the insertion of a stabilizer into an oversized bore and expanded into engagement with the surface of the bore. The stabilizers disclosed in U.S. Pat. Nos. 3,922,867 and 4,012,913 have tubes which are longitudinally slit so as to yield under circumferential compression to accommodate a forced insertion into an undersized bore. The slit stabilizers have a tendancy to fail when forceably inserted into a structure bore by a stabilizer driver, such driver normally being impacted by a piston. The slit, provided to accommodate a reduction of the cross-sectional dimension of the tube, opens up and the driven end of the tube bends and becomes splayed.
In U.S. Pat. No. 4,126,004, a wire rod is attached at the driven end of the tube so that the terminal surface and the wire rod provide an impact surface for accepting the impact forces. However, because of the structure of the wire rod, there is a considerable space between the terminal surface and the impact surface of the wire rod, whereby the terminal surface of the tube mushrooms upon initial impact forces until it substantially closes the gap and moves outwardly against the wire rod. This "mushrooming effect" adversely effects the distribution of the impact forces applied to the tube.